And which file formats and filesystems should that USB connection support? Should it support next-year's H269 format? Who will provide firmware updates to add new video formats?

That's my main objection to many of these all-in-one systems: the built-in technology support will be obsoleted before the rest of the system fails due to old age. I much prefer a dumb TV with a separate media box/dongle that I can replace with a new model every year to paying for a TV with soon-to-be-stale features.